Roman, you couldn't do that because you're just using the join function and printing the result. The point is the re-implement it completely.

Here's my try:

Python:

def join(lst, sep):
returnreduce(lambda x, y: x + sep + y, lst)

What I don't understand is, if we're not supposed to return anything or modifying any arguments, then what is the function supposed to do? Of course, there's probably some 'trick' that I'm missing completely.